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Abstract:

A pixel capable of displaying an image with uniform brightness is
disclosed. In one aspect, the pixel includes an organic light emitting
diode (OLED), a first transistor for controlling an amount of current
that flows from a first power supply to a second power supply via the
OLED in response to a voltage applied to a first node. The pixel also
includes a second transistor that is coupled between a bias power supply
and the first node and whose gate electrode is coupled to an emission
control line. The pixel further includes a third transistor that is
coupled between an anode electrode of the OLED and a feedback line and
whose gate electrode is coupled to a control line.

Claims:

1. A pixel, comprising: an organic light emitting diode (OLED); a first
transistor configured to control an amount of current that flows from a
first power supply to a second power supply via the OLED in response to a
voltage applied to a first node; a second transistor operatively coupled
between a bias power supply and the first node, wherein the second
transistor comprises a gate electrode coupled to an emission control
line; and a third transistor operatively coupled between an anode
electrode of the OLED and a feedback line, wherein the third transistor
comprises a gate electrode coupled to a control line.

2. The pixel as claimed in claim 1, wherein a voltage value of the bias
power supply is configured to be set so that an off bias voltage is
applied to the first transistor.

3. The pixel as claimed in claim 2, wherein the voltage of the bias power
supply is higher than the first power supply.

4. The pixel as claimed in claim 1, further comprising: a fourth
transistor operatively coupled between the first node and a data line,
wherein the fourth transistor comprises a gate electrode coupled to a
scan line; and a storage capacitor comprising a first terminal coupled to
the first node and a second terminal coupled to the first power supply.

5. The pixel as claimed in claim 4, wherein the second transistor is
configured to be turned on before the fourth transistor is turned on.

6. The pixel as claimed in claim 5, wherein the second transistor is
configured to be turned on after the fourth transistor is turned off.

7. The pixel as claimed in claim 5, wherein a turn on period of the
second transistor at least partially overlaps with a turn on period of
the fourth transistor.

8. The pixel as claimed in claim 7, wherein, when the turn on period of
the second transistor overlaps with the turn on period of the fourth
transistor, the bias power supply is configured to be set in a high
impedance state.

9. The pixel as claimed in claim 4, wherein the third transistor is
configured to be turned on in a partial period of a period in which the
second transistor is turned on in a specific frame period of a plurality
of frames.

10. The pixel as claimed in claim 4, further comprising: a fifth
transistor operatively coupled between a reference power supply and the
second terminal of the storage capacitor, wherein the fifth transistor
comprises a gate electrode coupled to the emission control line; a sixth
transistor operatively coupled between the first power supply and the
second terminal of the storage capacitor, wherein the sixth transistor
comprises a gate electrode coupled to an inverted emission control line;
and a seventh transistor operatively coupled between the first power
supply and the first transistor, wherein the seventh transistor comprises
a gate electrode coupled to the inverted emission control line.

11. The pixel as claimed in claim 10, wherein the sixth transistor and
the second transistor are configured to be alternately turned on and off.

12. The pixel as claimed in claim 10, wherein the second transistor is
configured to be turned on before the fourth transistor is turned on.

13. The pixel as claimed in claim 12, wherein the fourth transistor is
configured to be turned on so that the turn on period of the fourth
transistor at least partially overlaps with the turn on period of the
second transistor.

14. The pixel as claimed in claim 13, wherein, when the turn on period of
the second transistor overlaps with the turn on period of the fourth
transistor, the bias power supply is configured to be set in a high
impedance state.

15. The pixel as claimed in claim 10, wherein the third transistor is
configured to be turned on in a partial period of a period in which the
second transistor is turned on in a specific frame period of a plurality
of frames.

16. An organic light emitting display, comprising: a scan driver
configured to drive a plurality of scan lines and a plurality of emission
control lines; a data driver configured to drive a plurality of data
lines; a control line driver configured to drive a plurality of control
lines; a sensing unit coupled to a plurality of feedback lines; and a
plurality of pixels positioned at intersections of the scan lines and the
data lines, wherein each of pixels positioned in an ith (i is a natural
number) horizontal line comprises: an organic light emitting diode
(OLED); a first transistor configured to control an amount of current
that flows from a first power supply to a second power supply via the
OLED in response to a voltage applied to a first node; a second
transistor operatively coupled between a bias power supply and the first
node, wherein the second transistor is configured to be turned on when an
emission control signal is supplied to an ith emission control line, and
turned on in the other cases; and a third transistor operatively coupled
between an anode electrode of the OLED and a jth (j is a natural number)
feedback line, wherein the third transistor is configured to be turned on
when a control signal is supplied to an ith control line.

17. The organic light emitting display as claimed in claim 16, wherein a
voltage value of the bias power supply is configured to be set so that an
off bias voltage is applied to the first transistor.

18. The organic light emitting display as claimed in claim 17, wherein
the voltage of the bias power supply is higher than a voltage of the
first power supply.

19. The organic light emitting display as claimed in claim 16, wherein
each of the pixels positioned in the ith horizontal line further
comprises: a fourth transistor operatively coupled between the first node
and a jth data line and configured to be turned on when a scan signal is
supplied to an ith scan line; and a storage capacitor comprising a first
terminal coupled to the first node and a second terminal coupled to the
first power supply.

20. The organic light emitting display as claimed in claim 19, wherein
supply of an emission control signal to the ith emission control line is
configured to discontinue before a scan signal is supplied to the ith
scan line.

21. The organic light emitting display as claimed in claim 20, wherein
the emission control signal supplied to the ith emission control line at
least partially overlaps with the scan signal supplied to the ith scan
line.

22. The organic light emitting display as claimed in claim 20, wherein
the emission control signal supplied to the ith emission control line
does not overlap with the scan signal supplied to the ith scan line.

23. The organic light emitting display as claimed in claim 22, wherein
the bias power supply is configured to be set in a high impedance state
when the scan signal is supplied to the ith scan line.

24. The organic light emitting display as claimed in claim 20, wherein a
control signal is configured to be supplied to the ith control line not
to overlap with the emission control signal supplied to the ith emission
control line in a specific frame period of a plurality of frames.

25. The organic light emitting display as claimed in claim 19, further
comprising a plurality of inverted emission control lines driven by the
scan driver and formed to be coupled to the pixels in every horizontal
line.

26. The organic light emitting display as claimed in claim 25, wherein an
inverted emission control signal is configured to be supplied to an ith
inverted emission control line in the same period as the emission control
signal and has polarity inverted.

27. The organic light emitting display as claimed in claim 25, wherein
each of the pixels positioned in the ith horizontal line further
comprises: a fifth transistor operatively coupled between a reference
power supply and a second terminal of the storage capacitor, wherein the
fifth transistor is configured to be turned off when the emission control
signal is supplied to the ith emission control line; a sixth transistor
operatively coupled between the first power supply and a second terminal
of the storage capacitor, wherein the sixth transistor is configured to
be turned on when the inverted emission control signal is supplied to the
ith inverted emission control line, and turned off in the other cases;
and a seventh transistor operatively coupled between the first power
supply and the first transistor, wherein the seventh transistor is
configured to be turned on when the inverted emission control signal is
supplied to the ith inverted emission control line, and turned off in the
other cases.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to and the benefit of Korean
Patent Application No. 10-2012-0095477, filed on Aug. 30, 2012, in the
Korean Intellectual Property Office, the entire content of which is
incorporated herein by reference.

BACKGROUND

[0002] 1. Field

[0003] The described technology generally relates to a pixel and an
organic light emitting display using the same.

[0006] OLED displays display images using OLED that generate light by
re-combination of electrons and holes. The OLED display has high response
speed and is driven with low power consumption.

[0007] The OLED display includes a plurality of pixels arranged at
intersections of a plurality of data lines, scan lines, and power supply
lines in a matrix. Each of the pixels commonly includes an OLED and a
driving transistor for controlling the amount of current that flows to
the OLED. The pixels generate light components with predetermined
brightness components while supplying currents from the driving
transistors to the OLEDs to correspond to data signals.

SUMMARY

[0008] One inventive aspect is a pixel capable of displaying an image with
uniform brightness and an organic light emitting display using the same.

[0009] Another aspect is a pixel, including an organic light emitting
diode (OLED), a first transistor for controlling an amount of current
that flows from a first node to a second power supply via the OLED to
correspond to a voltage applied to a first node, a second transistor that
is coupled between a bias power supply and the first node and whose gate
electrode is coupled to an emission control line, and a third transistor
that is coupled between an anode electrode of the OLED and a feedback
line and whose gate electrode is coupled to a control line.

[0010] The voltage value of the bias power supply is set so that an off
bias voltage is applied to the first transistor. The voltage of the bias
power supply is set to be higher than the first power supply. The pixel
further includes a fourth transistor that is coupled between the first
node and a data line and whose gate electrode is coupled to a scan line
and a storage capacitor whose first terminal is coupled to the first node
and whose second terminal is coupled to the first power supply. The
second transistor may be turned on prior to the fourth transistor. The
second transistor may be turned on after the fourth transistor is turned
off. The turn on period of the second transistor may overlap with the
turn on period of the fourth transistor. When the turn on period of the
second transistor overlaps the turn on period of the fourth transistor,
the bias power supply is set in a high impedance state. The third
transistor is turned on in a partial period of a period in which the
second transistor is turned on in a specific frame period of a plurality
of frames.

[0011] The pixel further includes a fifth transistor that is coupled
between a reference power supply and a second terminal of the storage
capacitor and whose gate electrode is coupled to the emission control
line, a sixth transistor that is coupled between the first power supply
and the second terminal of the storage capacitor and whose gate electrode
is coupled to an inverted emission control line, and a seventh transistor
that is coupled between the first power supply and the first transistor
and whose gate electrode is coupled to the inverted emission control
line.

[0012] The sixth transistor and the second transistor are alternately
turned on and off. The second transistor is turned on prior to the fourth
transistor. The fourth transistor is turned on so that the turn on period
of the fourth transistor overlaps the turn on period of the second
transistor. When the turn on period of the second transistor overlaps the
turn on period of the fourth transistor, the bias power supply is set in
a high impedance state. The third transistor is turned on in a partial
period of a period in which the second transistor is turned on in a
specific frame period of a plurality of frames.

[0013] Another aspect is an organic light emitting display, including a
scan driver for driving scan lines and emission control lines, a data
driver for driving data lines, a control line driver for driving control
lines, a sensing unit coupled to feedback lines, and pixels positioned at
intersections of the scan lines and the data lines. Each of pixels
positioned in an ith (i is a natural number) horizontal line includes an
organic light emitting diode (OLED), a first transistor for controlling
an amount of current that flows from a first node to a second power
supply via the OLED to correspond to a voltage applied to a first node, a
second transistor coupled between a bias power supply and the first node,
turned on when an emission control signal is supplied to an ith emission
control line, and turned on in the other cases, and a third transistor
coupled between an anode electrode of the OLED and a jth (j is a natural
number) feedback line and turned on when a control signal is supplied to
an ith control line.

[0014] The voltage value of the bias power supply is set so that an off
bias voltage is applied to the first transistor. The voltage of the bias
power supply is higher than a voltage of the first power supply. Each of
the pixels positioned in the ith horizontal line further includes a
fourth transistor coupled between the first node and a jth data line and
turned on when a scan signal is supplied to an ith scan line and a
storage capacitor whose first terminal is coupled to the first node and
whose second terminal is coupled to the first power supply.

[0015] Supply of an emission control signal to the ith emission control
line is stopped before a scan signal is supplied to the ith scan line.
The emission control signal supplied to the ith emission control line
overlaps the scan signal supplied to the ith scan line. The emission
control signal supplied to the ith emission control line does not overlap
the scan signal supplied to the ith scan line. The bias power supply is
set in a high impedance state when the scan signal is supplied to the ith
scan line. A control signal is supplied to the ith control line not to
overlap the emission control signal supplied to the ith emission control
line in a specific frame period of a plurality of frames.

[0016] The organic light emitting display further includes inverted
emission control lines driven by the scan driver and formed to be coupled
to the pixels in every horizontal line. An inverted emission control
signal is supplied to an ith inverted emission control line in the same
period as the emission control signal and has polarity inverted. Each of
the pixels positioned in the ith horizontal line further includes a fifth
transistor coupled between a reference power supply and a second terminal
of the storage capacitor, turned off when the emission control signal is
supplied to the ith emission control line, a sixth transistor coupled
between the first power supply and a second terminal of the storage
capacitor, turned on when the inverted emission control signal is
supplied to the ith inverted emission control line, and turned off in the
other cases, and a seventh transistor coupled between the first power
supply and the first transistor, turned on when the inverted emission
control signal is supplied to the ith inverted emission control line, and
turned off in the other cases.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 is a view illustrating a deviation in brightness components
corresponding to gray scales.

[0018] FIG. 2 is a view illustrating an organic light emitting display
according to an embodiment.

[0019] FIG. 3 is a view illustrating a pixel according to a first
embodiment.

[0020]FIG. 4A is a view illustrating an embodiment of driving waveforms
supplied to the pixel of FIG. 3 in a driving period.

[0021]FIG. 4B is a view illustrating an embodiment of driving waveforms
supplied to the pixel of FIG. 3 in a sensing period.

[0022] FIG. 5A is a view illustrating another embodiment of driving
waveforms supplied to the pixel of FIG. 3 in the driving period.

[0023] FIG. 5B is a view illustrating another embodiment of driving
waveforms supplied to the pixel of FIG. 3 in the sensing period.

[0024] FIG. 6 is a view illustrating a pixel according to a second
embodiment.

[0025]FIG. 7A is a view illustrating an embodiment of driving waveforms
supplied to the pixel of FIG. 6 in the driving period.

[0026] FIG. 7B is a view illustrating an embodiment of driving waveforms
supplied to the pixel of FIG. 6 in the sensing period.

[0027] FIG. 8 is a view illustrating an organic light emitting display
according to another embodiment.

DETAILED DESCRIPTION

[0028] Generally, when a white gray scale is displayed after realizing a
black gray scale as illustrated in FIG. 1, light with lower brightness
than desired brightness is generated in a period of about two frames. In
this case, an image with desired brightness is not displayed by the
pixels to correspond to gray scales so that uniformity in brightness
deteriorates and that picture quality of a moving picture deteriorates.

[0029] As a result of experiment, deterioration of the response
characteristic of the organic light emitting display is caused by the
characteristic of the driving transistors included in the pixels. That
is, the threshold voltages of the driving transistors are shifted to
correspond to voltages applied to the driving transistors in a previous
frame period. Due to the shifted threshold voltages, light components
with desired brightness components are not generated in a current frame.

[0030] In addition, organic light emitting diodes (OLED) deteriorate in
proportion to the amount of use. When the OLEDs deteriorate due to a
change in efficiency, an image with desired brightness is not displayed.
This results in reduced brightness for the same data signal.

[0031] Hereinafter, embodiments will be described with reference to the
accompanying drawings. Here, when a first element is described as being
coupled to a second element, the first element may be not only directly
coupled to the second element but may also be indirectly coupled to the
second element via a third element. Further, some of the elements that
are not essential to the complete understanding of the present disclosure
are omitted for clarity. Also, like reference numerals refer to like
elements throughout.

[0032] Hereinafter, a pixel and an organic light emitting display using
the same will be described in detail as follows with reference to FIGS. 2
to 8.

[0033] FIG. 2 is a view illustrating an organic light emitting display
according to an embodiment.

[0034] Referring to FIG. 2, the organic light emitting display includes a
pixel unit 130 including pixels 140 positioned at the intersections of
scan lines S1 to Sn and data lines D1 to Dm, a scan driver 110 for
driving the scan lines S1 to Sn and emission control lines E1 to En, a
data driver 120 for driving the data lines D1 to Dm, a control line
driver 160 for driving control lines CL1 to CLn, and a timing controller
150 for controlling the scan driver 110, the data driver 120, and the
timing controller 150.

[0036] The pixel unit 130 includes the pixels 140 positioned at the
intersections of the scan lines S1 to Sn, the emission control lines E1
to En, the data lines D1 to Dm, feedback lines F1 to Fm, and the control
lines CL1 to CLn. The pixels 140 transmit the deterioration information
to the feedback lines F1 to Fm in a sensing period and receive data
signals corrected to correspond to the deterioration information in a
driving period. The pixels 140 that receive the data signals generate
light components with predetermined bright components while controlling
the amount of current supplied from a first power supply ELVDD to a
second power supply ELVSS via the OLEDs (not shown).

[0037] The scan driver 110 supplies scan signals to the scan lines S1 to
Sn and supplies emission control lines to the emission control lines E1
to En. Supply waveforms of the scan signals and the emission control
signals will be described later with reference to the drawings.

[0038] The control line driver 160 supplies control signals to the control
lines CL1 to CLn in the sensing period. For example, the control line
driver 160 may sequentially supply the control signals to the control
lines CL1 to CLn in the sensing period. The deterioration information on
the OLEDs provided in the pixels 140 is extracting in the sensing period.
Here, threshold voltage information on a driving transistor may be
further extracted in the sensing period to correspond to the structures
of the pixels 140.

[0039] The data driver 120 receives second data data2 in the driving
period and generates the data signals using the received second data
data2. The data signals generated by the data driver 120 are supplied to
the data lines D1 to Dm in synchronization with the scan signals.

[0040] The sensing unit 170 extracts the deterioration information on the
OLEDs and supplies the extracted deterioration information to the timing
controller 150 in the sensing period. That is, the sensing unit 170
extracts the deterioration information from the feedback lines F1 to Fm
in the sensing period. The sensing unit 170 may be realized by currently
published various types of circuits in order to compensate for
deterioration from the outside. Further, the sensing unit 170 may extract
the threshold voltages of driving transistors from the pixels 140.

[0041] The timing controller 150 controls the scan driver 110, the data
driver 120, and the control line driver 160. In addition, the timing
controller 150 changes first data data1 to correspond to the
deterioration information supplied from the sensing unit to generate the
second data data2. Here, the second data data2 is set so that the
deterioration information on the OLEDs provided in the pixels 140 may be
compensated for.

[0042] FIG. 3 is a view illustrating a pixel according to a first
embodiment. In FIG. 3, for convenience sake, the pixel connected to the
mth data line Dm and the nth scan line Sn will be illustrated.

[0043] Referring to FIG. 3, the pixel 140 according to the first
embodiment includes an organic light emitting diode (OLED) and a pixel
circuit 142 for supplying current to the OLED.

[0044] The anode electrode of the OLED is coupled to the pixel circuit 142
and the cathode electrode of the OLED is coupled to the second power
supply ELVSS. The OLED generates light with predetermined brightness to
correspond to current supplied from the pixel circuit 142.

[0045] The pixel circuit 142 supplies predetermined current to the OLED to
correspond to a data signal. Therefore, the pixel circuit 142 includes
first to fourth transistors M1 to M4 and a storage capacitor Cst.

[0046] The first electrode of the first transistor M1 is coupled to the
first power supply ELVDD and the second electrode of the first transistor
M1 is coupled to the anode electrode of the OLED. The first transistor M1
controls the amount of current supplied to the OLED to correspond to the
voltage applied to the gate electrode thereof, that is, a first node N1.

[0047] The first electrode of the second transistor M2 is coupled to the
first node N1 and the second electrode of the second transistor M2 is
coupled to a bias power supply Vbias. The gate electrode of the second
transistor M2 is coupled to the emission control line En. The second
transistor M2 is turned off when the emission control signal is supplied
to the emission control line En and is turned on when the emission
control signal is not supplied. On the other hand, the bias power supply
Vbias is set as a voltage at which the first transistor M1 may be turned
off, that is, an off bias voltage. For example, the bias power supply
Vbias is set as a higher voltage than the first power supply ELVDD.

[0048] The first electrode of the third transistor M3 is coupled to the
anode electrode of the OLED and the second electrode of the third
transistor M3 is coupled to the feedback line Fm. The gate electrode of
the third transistor M3 is coupled to the control line LCn. The third
transistor m3 is turned on when a control signal is supplied to the
control line CLn to electrically couple the feedback line Fm to the anode
electrode of the OLED.

[0049] The first electrode of the fourth transistor M4 is coupled to the
data line Dm and the second electrode of the fourth transistor M4 is
coupled to the first node N1. The gate electrode of the fourth transistor
M4 is coupled to the scan line Sn. The fourth transistor M4 is turned on
when the scan signal is supplied to the scan line Sn to electrically
couple the data line Dm to the first node N1.

[0050] The storage capacitor Cst is coupled between the first power supply
ELVDD and the first node N1. The storage capacitor Cst stores a voltage,
corresponding to the data signal.

[0051]FIG. 4A is a view illustrating an embodiment of driving waveforms
supplied to the pixel of FIG. 3 in a driving period. Here, in the driving
period, the pixel is normally driven.

[0052] Referring to FIG. 4A, first, in the first period T1, the emission
control signal is not supplied to the emission control line En so that
the second transistor M2 is turned on. When the second transistor M2 is
turned on, the voltage of the bias power supply Vbias is supplied to the
first node n1 so that the first transistor M1 is turned off. That is, in
the first period t1, the first transistor M1 (that is, a driving
transistor) receives an off bias voltage. In this case, the first
transistor M1 is initialized by the off bias voltage. Therefore, the
first transistor M1 may control the amount of current supplied to the
OLED so that an image with desired brightness is displayed regardless of
the data signal of a previous period.

[0053] Then, in a second period T2, the scan signal is supplied to the
scan line Sn. In the second period t2, the emission control signal is
supplied to the emission control line En. When the emission control
signal is supplied to the emission control line En, the second transistor
M2 is turned off. When the scan signal is supplied to the scan line Sn,
the fourth transistor M4 is turned on. When the fourth transistor M4 is
turned on, the data signal from the data line Dm is supplied to the first
node N1. At this time, the storage capacitor Cst charges the voltage
corresponding to the data signal. Then, the first transistor M1 supplies
the current stored in the storage capacitor Cst to the OLED so that light
with predetermined brightness is generated by the OLED.

[0054] In one embodiment, the pixels 140 repeat the above-described
processes in the driving period to realize a predetermined image. Here,
the above-described processes may be sequentially performed in units of
horizontal lines.

[0055]FIG. 4B is a view illustrating an embodiment of driving waveforms
supplied to the pixel of FIG. 3 in a sensing period. Here, in the sensing
period, the deterioration information on the OLED is extracted.

[0056] Referring to FIG. 4B, first, in a third period T3, the emission
control signal is not supplied to the emission control line En so that
the second transistor M2 is turned on. When the second transistor M2 is
turned on, the voltage of the bias power supply Vbias is supplied to the
first node N1 so that the first transistor M1 is turned off. That is, in
the third period T3, the first transistor M1 receives the off bias
voltage.

[0057] On the other hand, in the third period T3, the control signal is
supplied to the control line CLn in at least partial period so that the
third transistor M3 is turned on. When the third transistor M3 is turned
on, the feedback line Fm is electrically coupled to the anode electrode
of the OLED. In a period where the control signal is supplied to the
control line CLn, predetermined current is supplied from the sensing unit
170 to the feedback line Fm. The predetermined current supplied to the
feedback line Fm is supplied to the OLED so that a predetermined voltage
is applied to the OLED. Here, a resistance value changes to correspond to
the deterioration of the OLED. Therefore, the voltage applied to the OLED
to correspond to the predetermined current includes the deterioration
information on the OLED. The sensing unit 170 extracts the deterioration
information using the predetermined voltage applied to the OLED and
supplies the extracted deterioration information to the timing controller
150.

[0058] Then, in a fourth period T4, the scan signal is supplied to the
scan line Sn. In the fourth period t4, the emission control signal is
supplied to the emission control line En. When the emission control
signal is supplied to the emission control line En, the second transistor
M2 is turned off. When the scan signal is supplied to the scan line Sn,
the fourth transistor M4 is turned on. When the fourth transistor M4 is
turned on, the data signal from the data line Dm is supplied to the first
node N1. At this time, the storage capacitor Cst charges the voltage
corresponding to the data signal. Then, the first transistor M1 supplies
the current corresponding to the voltage stored in the storage capacitor
Cst to the OLED so that light with predetermined brightness is generated
by the OLED.

[0059] In one embodiment, the pixels 140 repeat the above-described
processes in the sensing period to realize a predetermined image. Here,
the above-described processes may be sequentially performed in units of
horizontal lines.

[0060] On the other hand, the driving period and the sensing period may be
properly arranged in units of frames. For example, in most frames, the
pixels are driven by the waveforms of the driving period and may be
driven by the waveforms of the sensing period. Then, in a specific frame,
the deterioration information is extracted from the OLED. Then, the
timing controller 150 changes the first data data1 so that the
deterioration of the OLEDs provided in the pixels 140 may be compensated
for using the deterioration information to generate the second data
data2. Therefore, in the driving period, an image with uniform brightness
may be achieved by the pixels 140 regardless of the deterioration of the
OLEDs.

[0061] FIG. 5A is a view illustrating another embodiment of driving
waveforms supplied to the pixel of FIG. 3 in the driving period. In FIG.
5A, detailed description of the same elements as the elements of FIG. 4A
will be omitted. A difference between FIGS. 4A and 4B and FIGS. 5A and 5B
lies in that the emission control signals and the scan signals overlap
each other in FIGS. 4A and 4B and that the emission control signals and
the scan signals do not overlap each other.

[0062] Referring to FIG. 5A, first, in a first period T1', the second
transistor M2 is turned on so that an off bias voltage is supplied to the
first transistor M1.

[0063] Then, in a second period T2', the scan signal is supplied to the
scan line Sn. Here, the emission control signal is not supplied to the
emission control line En in a period where the scan signal is supplied to
the scan line Sn. In this case, in the period where the scan signal is
supplied to the scan line Sn, the second transistor M2 and the fourth
transistor M4 are turned on.

[0064] When the fourth transistor M4 is turned on, the data signal from
the data line Dm is supplied to the first node N1. At this time, the
storage capacitor Cst charges the voltage corresponding to the data
signal. On the other hand, in the period where the scan signal is
supplied to the scan line Sn, the bias power supply Vbias is set in a
high impedance Hi-z state. Therefore, in the period where the scan signal
is supplied to the scan line Sn, although the second transistor M2 is
turned on, the storage capacitor Cst may stably charge the voltage
corresponding to the data signal.

[0065] After the voltage is stored in the storage capacitor Cst, supply of
the scan signal to the scan line Sn is stopped so that the fourth
transistor M4 is turned off and the emission control signal is supplied
to the emission control line En so that the second transistor M2 is
turned off. Then, the first transistor M1 supplies the current
corresponding to the voltage stored in the storage capacitor Cst to the
OLED so that light with predetermined brightness is generated by the
OLED.

[0066] FIG. 5B is a view illustrating another embodiment of driving
waveforms supplied to the pixel of FIG. 3 in the sensing period. In FIG.
5B, detailed description of the same elements as the elements of FIG. 4B
will be omitted.

[0067] Referring to FIG. 5B, first, in a third period T3', the second
transistor M2 is turned on so that an off bias voltage is supplied to the
first transistor M1. In the third period T3', the third transistor M3 is
turned on to correspond to the control signal supplied to the control
line CLn. In the period where the third transistor M3 is turned on, the
sensing unit 170 extracts the deterioration information on the OLED using
the voltage applied to the OLED to correspond to predetermined current.

[0068] Then, in a fourth period T4', the scan signal is supplied to the
scan line Sn. Here, the emission control signal is not supplied to the
emission control line En in a period where the scan signal is supplied to
the scan line Sn. In this case, in the period where the scan signal is
supplied to the scan line Sn, the second transistor M2 and the fourth
transistor M4 are turned on.

[0069] When the fourth transistor M4 is turned on, the data signal from
the data line Dm is supplied to the first node N1. At this time, the
storage capacitor Cst charges the voltage corresponding to the data
signal. On the other hand, in the period where the scan signal is
supplied to the scan line Sn, the bias power supply Vbias is set in a
high impedance Hi-z state. Therefore, in the period where the scan signal
is supplied to the scan line Sn, although the second transistor M2 is
turned on, the storage capacitor Cst may stably charge the voltage
corresponding to the data signal.

[0070] After the voltage is stored in the storage capacitor Cst, supply of
the scan signal to the scan line Sn is stopped so that the fourth
transistor M4 is turned off and the emission control signal is supplied
to the emission control line En so that the second transistor M2 is
turned off. Then, the first transistor M1 supplies the current
corresponding to the voltage stored in the storage capacitor Cst to the
OLED so that light with predetermined brightness is generated by the
OLED.

[0071] FIG. 6 is a view illustrating a pixel according to a second
embodiment. In FIG. 6, for convenience sake, the pixel connected to the
mth data line Dm and the nth scan line Sn will be illustrated. In FIG. 6,
the same elements as the elements of FIG. 3 are denoted by the same
reference numerals and detailed description thereof will be omitted.

[0072] Referring to FIG. 6, the pixel 140 according to the second
embodiment includes an organic light emitting diode (OLED) and a pixel
circuit 142' for supplying current to the OLED.

[0073] The anode electrode of the OLED is coupled to the pixel circuit
142' and the cathode electrode of the OLED is coupled to the second power
supply ELVSS. The OLED generates light with predetermined brightness to
correspond to current supplied from the pixel circuit 142'.

[0074] The pixel circuit 142' supplies predetermined current to the OLED
to correspond to a data signal. Therefore, the pixel circuit 142'
includes first to seventh transistors M1 to M7 and a storage capacitor
Cst'.

[0075] The first terminal of the storage capacitor Cst' is coupled to the
first node N1 and the second terminal of the storage capacitor Cst' is
coupled to the second node N2. The storage capacitor Cst' charges a
voltage corresponding to the data signal.

[0076] The first electrode of the fifth transistor M5 is coupled to a
reference power supply Vref and the second electrode of the fifth
transistor M5 is coupled to the second node N2. The gate electrode of the
fifth transistor M5 is coupled to the emission control line En. The fifth
transistor M5 is turned off when the emission control signal is supplied
to the emission control line En and is turned on in the other cases.

[0077] The first electrode of the sixth transistor M6 is coupled to the
first power supply ELVDD and the second electrode of the sixth transistor
M6 is coupled to the second node N2. The gate electrode of the sixth
transistor M6 is coupled to an inverted emission control line /En. The
sixth transistor M6 is turned on when an inverted emission control signal
is supplied to the inverted emission control line /En and is turned off
in the other cases.

[0078] Here, the inverted emission control signal is supplied to the
inverted emission control line /En in the same period as the emission
control signal supplied to the emission control line En and the polarity
of the emission control signal is opposite to the polarity of the
inverted emission control signal as illustrated in FIGS. 7A and 7B. That
is, the emission control signal is set as a high voltage at which the
transistors may be turned off and the inverted emission control signal is
set as a low voltage at which the transistors may be turned on. For
example, the inverted emission control signal supplied to an ith (i is a
natural number) inverted emission control line Ei may be generated by
inverting the emission control signal supplied to the ith emission
control line Ei. Additionally, when the pixel of FIG. 6 is applied,
inverted emission control lines /E1 to /En are additionally formed in
every horizontal line like the emission control lines E1 to En as
illustrated in FIG. 8.

[0079] The first electrode of the seventh transistor M7 is coupled to the
first power supply ELVDD and the second electrode of the seventh
transistor M7 is coupled to the first electrode of the first transistor
M1. The gate electrode of the seventh transistor M7 is coupled to the
inverted emission control line /En. The seventh transistor M7 is turned
on when the inverted emission control signal is supplied to the inverted
emission control line /En and is turned off in the other cases.

[0080]FIG. 7A is a view illustrating an embodiment of driving waveforms
supplied to the pixel of FIG. 6 in the driving period.

[0081] Referring to FIG. 7A, first, in an eleventh period T11, the
emission control signal is not supplied to the emission control line En
and the inverted emission control signal is not supplied to the inverted
emission control line/En. When the emission control signal is not
supplied to the emission control line En, the second transistor M2 and
the fifth transistor M5 are turned on. When the second transistor M2 is
turned on, the voltage of the bias power supply Vbias is supplied to the
first node N1. When the fifth transistor M5 is turned on, the voltage of
the reference power supply Vref is supplied to the second node N2.

[0082] When the voltage of the bias power supply Vbias is supplied to the
first node N1, in the eleventh period T11, the first transistor M1
receives an off bias voltage. In this case, the first transistor M1 is
initialized by the off bias voltage.

[0083] Then, in a twelfth period T12, the scan signal is supplied to the
scan line Sn. When the scan signal is supplied to the scan line Sn, the
fourth transistor M4 is turned on. When the fourth transistor M4 is
turned on, the data signal from the data line Dm is supplied to the first
node N1. At this time, since the fifth transistor M5 is turned on, the
storage capacitor Cst' charges a voltage corresponding to a difference
between the reference power supply Vref and the data signal.

[0084] Here, the reference power supply Vref is not dropped to the voltage
of the power supply at which current is not supplied to the pixels.
Therefore, a desired voltage may be charged in the storage capacitor Cst'
regardless of the voltage drop of the first power supply ELVDD. The
voltage of the reference power supply Vref may have various values in
comparison with the data signal. For example, the voltage of the
reference power supply Vref may have the same value as the first power
supply ELVDD.

[0085] In the period where the scan signal is supplied to the scan line
Sn, the bias power supply Vbias is set in the high impedance state. In
this case, a desired voltage may be charged in the storage capacitor Cst'
regardless of whether the second transistor M2 is turned on.

[0086] After a predetermined voltage is charged in the storage capacitor
Cst', the emission control signal is supplied to the emission control
line En and the inverted emission control signal is supplied to the
inverted emission control line /En. When the emission control signal is
supplied to the emission control line En, the second transistor M2 and
the fifth transistor M5 are turned off. When the inverted emission
control signal is supplied to the inverted emission control line /En, the
sixth transistor M6 and the seventh transistor M7 are turned on.

[0087] When the sixth transistor M6 is turned on, the second node N2 and
the first power supply ELVDD are electrically coupled to each other. At
this time, since the first node n1 is floated, the storage capacitor Cst'
maintains a voltage charged in a previous period. When the seventh
transistor M7 is turned on, the first transistor M1 and the first power
supply ELVDD are electrically coupled to each other. At this time, the
first transistor M1 controls the amount of current that flows from the
first power supply ELVDD to the second power supply ELVSS via the OLED to
correspond to the voltage applied to the first node N1.

[0088] In one embodiment, the pixels 140 repeat the above-described
processes in the driving period to realize a predetermined image. Here,
the above-describe processes may be sequentially performed in units of
horizontal lines.

[0089] FIG. 7B is a view illustrating an embodiment of driving waveforms
supplied to the pixel of FIG. 6 in the sensing period.

[0090] Referring to FIG. 7B first, in a thirteenth period T13, the
emission control signal is not supplied to the emission control line En
and the inverted emission control signal is not supplied to the inverted
emission control line /E. When the emission control signal is not
supplied to the emission control line En, the second transistor M2 and
the fifth transistor M5 are turned on. When the second transistor M2 is
turned on, the voltage of the bias power supply Vbias is supplied to the
first node N1. When the fifth transistor M5 is turned on, the voltage of
the reference power supply Vref is supplied to the second node N2.

[0091] When the voltage of the bias power supply Vbias is supplied to the
first node N1, in the thirteenth period T13, the first transistor M1
receives an off bias voltage. In this case, the first transistor M1 is
initialized by the off bias voltage.

[0092] On the other hand, in at least partial period of the thirteenth
period T13, the control signal is supplied to the control line CLn so
that the third transistor M3 is turned on. When the third transistor M3
is turned on, the feedback line Fm is electrically coupled to the anode
electrode of the OLED. Then, a predetermined voltage is applied to the
anode electrode of the OLED to correspond to predetermined current
supplied from the sensing unit 170 and the sensing unit 170 extracts the
deterioration information from the predetermined voltage applied to the
OLED.

[0093] Then, in a fourteenth period T14, the scan signal is supplied to
the scan line Sn. When the scan signal is supplied to the scan line Sn,
the fourth transistor M4 is turned on. When the fourth transistor M4 is
turned on, the data signal from the data line Dm is supplied to the first
node N1. At this time, since the fifth transistor M5 is turned on, the
storage capacitor Cst' charges the voltage corresponding to the
difference between the reference power supply Vref and the data signal.

[0094] In the period where the scan signal is supplied to the scan line
Sn, the bias power supply Vbias is set in the high impedance state. In
this case, a desired voltage may be charged in the storage capacitor Cst'
regardless of whether the second transistor M2 is turned on.

[0095] After the predetermined voltage is charged in the storage capacitor
Cst', the emission control signal is supplied to the emission control
line En and the inverted emission control signal is supplied to the
inverted emission control line /En. When the emission control signal is
supplied to the emission control line En, the second transistor M2 and
the fifth transistor M5 are turned off. When the inverted emission
control signal is supplied to the inverted emission control line /En, the
sixth transistor M6 and the seventh transistor M7 are turned on.

[0096] When the sixth transistor M6 is turned on, the second node N2 and
the first power supply ELVDD are electrically coupled to each other. At
this time; since the first node n1 is floated, the storage capacitor Cst'
maintains a voltage charged in a previous period. When the seventh
transistor M7 is turned on, the first transistor M1 and the first power
supply ELVDD are electrically coupled to each other. At this time, the
first transistor M1 controls the amount of current that flows from the
first power supply ELVDD to the second power supply ELVSS via the OLED to
correspond to the voltage applied to the first node N1.

[0097] In one embodiment, the pixels 140 repeat the above-described
processes in the driving period to realize a predetermined image. Here,
the above-describe processes may be sequentially performed in units of
horizontal lines.

[0098] According to at least one of the disclosed embodiments, the off
bias voltage is applied to the driving transistor before the data signal
is supplied to initialize the characteristic of the driving transistor.
In this case, the driving transistor may supply desired current to the
OLED regardless of the data signal of a previous period so that an image
with uniform brightness is displayed. In addition, deterioration
information on the OLED is extracted and data is changed in response to
the extracted information so that an image with uniform brightness is
displayed regardless of the deterioration of the OLED.

[0099] While the above embodiments have been described in connection with
the accompanying drawings, it is to be understood that the present
disclosure is not limited to the disclosed embodiments, but, on the
contrary, is intended to cover various modifications and equivalent
arrangements included within the spirit and scope of the appended claims,
and equivalents thereof.